Specifications
GAL20VP8
Output Logic Macrocell (OLMC)
The following discussion pertains to configuring the output logic
macrocell. It should be noted that actual implementation is accom-
plished by development software/hardware and is completely trans-
parent to the user.
There are three global OLMC configuration modes possible:
simple, complex,
and
registered.
Details of each of these modes
is illustrated in the following pages. Two global bits, SYN and AC0,
control the mode configuration for all macrocells. The XOR bit of
each macrocell controls the polarity of the output in any of the three
modes, while the AC1 and AC2 bit of each of the macrocells controls
the input/output and totem-pole/open-drain configuration. These
two global and 24 individual architecture bits define all possible con-
figurations in a GAL20VP8. The information given on these archi-
tecture bits is only to give a better understanding of the device.
Compiler software will transparently set these architecture bits from
the pin definitions, so the user should not need to directly manipulate
these architecture bits.
Compiler Support for OLMC
Software compilers support the three different global OLMC modes
as different device types. Most compilers also have the ability to
automatically select the device type, generally based on the register
usage and output enable (OE) usage. Register usage on the device
forces the software to choose the registered mode. All combina-
torial outputs with OE controlled by the product term will force the
software to choose the complex mode. The software will choose
the simple mode only when all outputs are dedicated combinatorial
without OE control. For further details, refer to the compiler soft-
ware manuals.
When using compiler software to configure the device, the user
must pay special attention to the following restrictions in each mode.
In
registered mode
pin 1(2) and pin 12(14) are permanently con-
figured as clock and output enable, respectively. These pins cannot
be configured as dedicated inputs in the registered mode.
In
complex mode
pin 1(2) and pin 12(14) become dedicated in-
puts and use the feedback paths of pin 22(26) and pin 14(17) re-
spectively. Because of this feedback path usage, pin 22(26) and
pin 14(17) do not have the feedback option in this mode.
In
simple mode
all feedback paths of the output pins are routed
via the adjacent pins. In doing so, the two inner most pins (pins
17(20) and 19(23)) will not have the feedback option as these pins
are always configured as dedicated combinatorial output.
In addition to the architecture configurations, the logic compiler
software also supports configuration of either totem-pole or open-
drain outputs. The actual architecture bit configuration, again, is
transparent to the user with the default configuration being the
standard totem-pole output.
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LATTICE [ LATTICE SEMICONDUCTOR ]
